USB Audio doesn't work?

I just bought a Fiio K1 USB dac/amp to use with my laptop, but I also read that it works with some smartphones via an OTG cable. So I hooked it up to my S6 with my OTG cable and it didn't work. Sometimes I would hear a weird static noise, but otherwise my music wouldn't come through any output while the K1 was plugged in. I then tried my same OTG cable and K1 with a friend's Verizon S6 and it worked flawlessly. Both of our phones are running Android 5.1.1. What's going on? Did Sprint butcher USB audio on the S6 with their custom ROM? I'm really disappointed.

If anyone has gotten USB dacs to work with their Sprint S6, was there anything special you had to do first?

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